Mechanical Ventilation System

Mechanical ventilation systems transmit fresh air using ducts and fans, without purely depending on air via tiny openings in walls. The necessary fans and conditioning equipment are generally located in separate plant rooms, often in a very large, extend throughout the building, penetrate compartment walls and/or floors and have openings in every space through which it passes.

In the absence of fire precautions, ventilation ductwork furnishes a route by which fire, smoke, and toxic gases are enabled to escalate through a building.

Smoke Extraction Systems

The main objective of a smoke extraction system is to avert danger, i.e. to save lives and to protect property. The smoke extraction system facilitates the escape of the building occupants and assists firefighters in locating the actual location of the fire and extinguishing it.

If the ductwork is incorporated in a smoke extraction system is wholly contained within the fire compartment, it must at least be capable of resisting the anticipated smoke temperatures generated during the development of a fire. These will generally be lower than the temperatures specified in BS 476: Part 24, which are intended to represent a fully developed fire. However, if the ductwork penetrates a fire resisting barrier, it must also be capable of providing the relevant fire resistance in a test to Part 24. Further clarification of the fire testing requirements for these two different situations is provided in Section ‘5’ of this document ‘Standard Fire Tests’. In view of the importance of maintaining the design extraction rates during a fire, Part 24 also imposes an additional requirement on smoke outlet ductwork (i.e. the retention of at least 75% of its original sectional area during the test)

Car Park and Kitchen Extraction Systems

Car parks and non-domestic kitchens are required to have separate and independent extraction systems, because of the polluted nature of the extracted air. As BS 5588: Part 9/BS9999, recommends that fire dampers should not be installed in extraction ductwork serving car parks or kitchens, any duct or ductwork penetrating fie resisting barriers should be fire resisting.

Kitchen extraction ductwork should be subjected to regular safety checks to prevent any hazards. A fire in an adjacent compartment through which the ductwork passes could, therefore, initiate a fire within the ductwork which, in the absence of fire dampers, might jeopardise the safety of the kitchen occupants. As a result, BS 476: Part 24 sets an additional requirement, (i.e when tested as duct A against external fire) the internal surface of the ductwork within the furnace must meet the insulation criteria. It is also essential that this particular type of ductwork is provided with access for cleaning, at distances not exceeding 3m.

Dual Ventilation/Smoke Extraction Systems

These systems serve as a conventional ventilation system under normal conditions but are converted to a smoke extraction system in the event of a fire, thus providing an economical dual system.